1. Field of the Invention
The present invention relates to a multilayer transformer component used as, e.g., a balun transformer and a common-mode choke coil.
2. Description of the Related Art
Demands for smaller sizes and higher density have increased in the field of transformer components. To meet these demands, a multilayer transformer component is proposed which is formed by, e.g., photolithography capable of performing microfabrication (see, for example, Japanese Unexamined Patent Application Publication No. 2005-158975).
FIG. 16 is a perspective view of a known multilayer transformer component, the view illustrating coil portions in a see-through manner, and FIGS. 17A and 17B are plan views illustrating connection states of external electrodes and coils.
As illustrated in FIG. 16, a multilayer transformer component 100 includes a primary-side coil 101 and a secondary-side coil 102 that are disposed in an insulator 110 which is sandwiched between magnetic base plates, and external electrodes 121 to 124 provided on an outer surface of such a chip body that are connected to the primary-side and secondary-side coils 101, 102.
More specifically, as illustrated in FIG. 17A, an outer end 101a and an inner end 101b of the primary-side coil 101 are respectively connected to the external electrodes 121 and 123, which are arranged opposite to each other. Also, as illustrated in FIG. 17B, an outer end 102a and an inner end 102b of the secondary-side coil 102 are respectively connected to the external electrodes 122 and 124, which are arranged opposite to each other.
However, the above-described known multilayer transformer component 100 has the following problems.
In the known multilayer transformer component 100, the outer end 101a and the inner end 101b of the primary-side coil 101 are respectively connected to the external electrodes 121 and 123, which are arranged opposite to each other, as illustrated in FIG. 17A, and the outer end 102a and the inner end 102b of the secondary-side coil 102 are respectively connected to the external electrodes 122 and 124, which are arranged opposite to each other, as illustrated in FIG. 17B. Therefore, a difference occurs between an inductance value of the primary-side coil 101 and an inductance value of the secondary-side coil 102.
More specifically, as illustrated in FIG. 17A, because a current I flowing through an intermediate portion 101c extending from a coil body of the primary-side coil 101 to the outer end 101a is in a reverse direction from the current I flowing through a body portion 101e of the primary-side coil 101, an inductance value of the intermediate portion 101c is significantly reduced due to the cancellation of magnetic forces. Furthermore, because the current I flowing through an intermediate portion 101d extending from the coil body to the inner end 101b is in a reverse direction from the current I flowing through the body portion 101e, an inductance value of the intermediate portion 101d is also significantly reduced.
In the secondary-side coil 102, as illustrated in FIG. 17B, a portion in which a current flows in a reverse direction from that of the current flowing through an intermediate portion 102c extending from a coil body of the secondary-side coil 102 to the outer end 102a is not present near the intermediate portion 102c. Furthermore, a current flowing in a reverse direction from that of the current flowing through an intermediate portion 102d extending from the coil body to the inner end 102b is also not present near the intermediate portion 102d. Thus, a portion in which an inductance value is significantly reduced by the cancellation of magnetic forces is not present. Accordingly, the inductance value of the secondary-side coil 102 is greater than that of the primary-side coil 101.
In the multilayer transformer component 100, as described above, because a difference occurs in inductance value between the primary-side coil 101 and the secondary-side coil 102, an insertion loss characteristic of the multilayer transformer component 100 differs depending on a mounting direction. Therefore, when the multilayer transformer component 100 is used as a common-mode choke coil, a noise removing effect also differs depending on the mounting direction. When the multilayer transformer component 100 is used as a balun transformer, there is a risk that characteristics of an output signal differ depending on the mounting direction and a characteristic variation increases.